The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
A powertrain includes a torque generative device providing torque to a rotating member. A hybrid powertrain utilizes at least two torque generative devices, for example an internal combustion engine and one or more electric machines. A hybrid transmission is employed and configured to selectively receive and transmit torque through the various gear members and change gear states to establish a relationship between a rotational input to the transmission and a rotational output of the transmission.
It is known to employ diesel combustion engines due to their ability to produce desirable torque utilizing air-fuel ratios that are lean of stoichiometry. While the lean air-fuel ratios provide increased fuel economy compared to gasoline engines, emissions efficiency is reduced due to increased levels of NOx and hydrocarbons output from the diesel engine. Accordingly, if the diesel engine is optimized to obtain the greatest fuel efficiency, increased levels of emissions may result. Additionally, fuel economy can be reduced indirectly if aftertreatment systems require frequent cleaning and regeneration.
It is known to optimize the impact of emissions in diesel engines by maintaining an optimal or desired air-fuel ratio. Because an injected fuel mass is established to meet a desired axle torque requested by an operator of a vehicle, intake air mass must be adjusted to maintain the desired air-fuel ratio for a specific engine operating point. One drawback of maintaining the desired air-fuel ratio to meet emissions standards is that drivability can be sacrificed due to a time delay associated with adjusting the intake air mass through delays in adjusting levels of exhaust gas recirculation, turbocharging, and/or throttle opening.